This invention relates generally to additive manufacturing and, in particular, to the fabrication of machine-readable codes such as one or two-dimensional barcodes using closed-loop, laser-based, direct metal deposition (DMD(trademark)).
Compared to one-dimensional barcodes of the type found on grocery items and consumer products, two-dimensional barcodes are now recognized as a way of automatically identifying objects with much greater information content. One- and two-dimensional codes are now used on many engineering components to track genesis and to prevent proliferation of poor-quality copies. Many of these components are expensive yet rendered obsolete after a modest service life due to hostile operating conditions. The desired durability of machine-readable codes on components depends on service conditions and applications. However, if the coding system cannot survive such environment, the history of origin cannot be tracked for proper replacement.
Different two-dimensional bar codes are in use, including the codes devised by Data Matrix International, as described in U.S. Pat. No. 5,053,609 and the patents which depend therefrom, all of which are incorporated herein by reference. Presently Data Matrix codes are marked in several ways, including:
1) Laser marking: Surface changes are made by focusing laser energy to cause one or more of the following:
a) Surface etching;
b) Surface annealing and burning which changes surface reflectance; and
c) Engraving.
2) Dot Peening: In this process, a marker stylus is pressed against the surface of the material to create an indentation. Colors can be added to these depressions to improve contrast. Typical resolutions of these marking are in the order of 250 micrometers wide and 100 micrometers deep.
3) Ink Jet Printers: In this method, ink is sprayed from a printer head to an article surface to create marks. The longevity of the mark depends on the chemical reaction of the ink with the substrate.
The permanence of all three processes described above is limited in severe reactive environment and high-temperature environments due to shallow surface penetration or possible reaction with the environment. Earth moving and rotating components are subjected to high wear and erosion environment. Certain aircraft components have a service life exceeding 30 years and such durable codes are valuable in tracking history in case of replacement or accident. Turbines for aircraft and power generation are exposed to both high-temperature and oxidizing atmospheres. The ability to survive under such conditions is critical for future identification of the components after years of service.
A method of material deposition capable of enduring hostile and/or high temperature environment directly from digital data will resolve this xe2x80x9cservice longevityxe2x80x9d issue.
According to this invention, direct metal deposition (DMD(trademark)) is used to deposit machine-readable codes onto articles with high accuracy, directly from digital data. In the preferred embodiment, a closed-loop DMD process is used to achieve high accuracy and resolution. The use of DMD also offers a large portfolio of deposition materials, including nickel super alloys for withstanding hostile and high-temperature environments, and H13 tool steel for high wear resistance. In the case of lightweight aircraft components made with aluminum and titanium, the process can be used to deposit Al and Ti, as well as more durable Al and Ti alloys. Moreover, as the technology of symbology improves to include three-dimensional features, DMD, particularly CLDMD, will be used to deposit predetermined heights with well-defined widths and spacings to open up a new dimension in coding systems.
According to the method of the invention, one or more layers of material are deposited onto the surface of an article using the laser-assisted DMD process to achieve desired dimensional characteristics. In different embodiments, the substrate/layer combination may be tailored for improved wear resistance, thermal conductivity, density/hardness, corrosion and/or resistance to corrosion, oxidation or other environmental conditions. Alternatively, the layer(s) of material may be tailored to have specific properties custom-tailored to suit the application.
In the preferred embodiment, a closed-loop, laser-assisted DMD process is deployed to write the symbol on the component substrate on an incremental basis using the digital data from the code generation program. To enhance throughput, code features may be fabricated using a robotic closed-loop DMD arrangement. In concert with the improvements made possible through the tailored outer layer(s), the method may further include the step of incorporating a third dimension by controlling the height of the deposit line in addition to the width. Indeed, as opposed to, or in conjunction with, a computer-readable code, the method and apparatus of the invention may be used to construct a one- or multi-dimensional xe2x80x9ctest regionxe2x80x9d on an article or substrate, enabling human or machine visualization to determine the level of wear, service, corrosion, remaining life, and so forth, by viewing and analyzing the degradation of one or more deposited features, whether of the same or different material composition.